Known types of vial closure caps suffer from problems. One such known closure cap makes use of a rubber plug stopper which after insertion into the open end of the vial has its upper portion completely covered and surrounded by a thin aluminum sheath. The top of the aluminum sheath and a small portion of the surrounding aluminum skirt are scored to enable the insertion of a fingernail to thereby tear the thin aluminum sheath and remove it from the rubber stopper. In practice, the aluminum sheath does not always completely separate from the rubber stopper and the technician often suffers finger cuts from the sharp edges of the aluminum residue which surrounds the stopper. Other problems with this particular type of closure cap are: the fingernail inserted into the scored portion of the aluminum sheath may break, and the removal of the rubber plug stopper sometimes causes the liquid contents (often a blood solution) of the vial to splash onto the person opening the vial.
Another known closure cap is described in U.S. Pat. No. 3,540,612 granted to William T. Brady, Nov. 17, 1970. This patent discloses a closure cap having a frustoconical section connected to a closed end plug section to form a one-piece cap. The plug section has a bead thereon removed from the distal end thereof. All parts of this particular cap are made of the same deformable material which material bulges when the cap is tightened on the vial. Although the patent falls to describe the particular material from which the entire cap is made, it is quite clear that it is a plastic, such as a copolymer, which deforms partially plastically and partially elastically, as evidenced by the commercially available bottle caps incorporating the patented invention. Disadvantages of this known cap are: The torque required to open and close the bottle cap during repeated uses of the cap tends to cause the deformable plastic material to retain the shape into which it has been deformed once it has been initially used, thereby interfering with a perfect seal upon re-use of the cap. Since the screw-type cover part and the closed end plug of the one-piece cap are made of the same deformable material, the screw threads of the cover tend to deform permanently upon repeated threading and rethreading of the cap on the bottle until finally tightening of the cap on the bottle does not produce sufficient downward pressure to assure a proper air and liquid-tight seal with the bottle. The space between the bead and the bottom of the plug constitutes a blood catching intersection area which promotes clotting and coagulation of the blood, thereby interfering with accurate repeatable instrument counter readings and measurements of the blood solution until the vial contents are entirely depleted.